WESTERN A rborist Fusarium dieback: A new and serious insect-vectored disease of landscape trees Donald R. Hodel, Angela Liu, Gevork Arakelian, Akif Eskalen, Richard Stouthamer

new, serious, insect- many common landscape trees and americana, and some other species, a vectored disease, Fusarium avocado and other fruit trees. Here white, sometimes crusty ring or halo dieback, has been dis- we provide a brief overview of the of sugary exudate surrounds the Acovered in southern California on disease and its vector. entry/exit hole (Figs. 6). Scraping landscape trees and Persea americana the bark down to the wood behind (avocado). The latter is typically Disease symptoms the entry/exit hole reveals brown an orchard tree but, because of the Symptoms of Fusarium dieback in- necrotic tissue (Fig. 7). Staining may popularity of its fruit, it frequently clude dark, dry or water-soaked or be found beneath the outermost lay- appears in the landscape. A new, yet oily-looking, sometimes weeping le- ers of sapwood to a depth of up to 1.5 unnamed species of Fusarium causes sions surrounding beetle entry/exit to 2 inches. So far the disease has only the disease. A type of ambrosia beetle holes on the trunk and branches been found in Israel and California. tentatively identified as the tea shot (Figs. 1-3); discolored wood; leaf hole borer (TSHB) is the vector al- discoloration and chlorosis; wilt- Tea Shot Hole Borer though the beetle, morphologically ing; branch dieback (Fig. 4); and, in The TSHB (Euwallacea fornicatus) is identical to the TSHB, might also be some cases, death of the tree (Fig. 5). native to southern Asia. Initially it a new species. The host list includes In Acer negundo (box elder), Persea was collected and described from Ceylon (Sri Lanka) in 1868. It has been found in Bangladesh, Cambodia, Figure 1. (Left) On this old Acer negundo in Long Beach, CA initial symptoms of China, Japan, India, Indonesia, Ma- Fusarium dieback include dark, discolored, dry or water-soaked or oily-look- laysia, Myanmar, Taiwan, Thailand, ing, sometimes weeping bark lesions surrounding beetle entry/exit holes on the Vietnam, New Guinea, Philippine trunk and branches. (D. R. Hodel). Islands, Fiji, Samoa, Reunion Island, Figure 2. (Right) Extensive areas of discolored, dry or water-soaked or oily-look- Micronesia, Australia, Israel, Mada- ing lesions, which give the bark a somewhat stained appearance, are symptoms gascar, Panama, and the United States of Fusarium dieback on this young, severely attacked Acer negundo in Long including Florida, Hawaii, and, most Beach, CA. Note the chlorotic leaves. (D. R. Hodel). recently, California. The TSHB favors tropical and subtropical climates, where it produces multiple genera- tions per year, but has been found at elevations of up to 15,000 feet. It is considered an aggressive pest and can attack healthy, vigorous trees as well as weakened or stressed trees. An unusually small beetle, female TSHBs are 0.07 to 0.1 inch long and dark brown to black (Fig. 8) while males are even smaller, about 0.05 inch long and brown (Fig. 9). The female TSHB is the primary disperser and, once landing on a new host tree, it makes tunnels by burrowing through the bark and into the wood, penetrating about 0.5 to 1.5 inches. Entry/exit holes in avocadoes are about 0.033 inch in diameter. Larvae are about 0.14 inch long and 0.04 inch wide. In heavy, severe infestations,

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Figure 3. (Left) Extensive areas of discolored, dry or water-soaked or oily-looking lesions, which give the bark a somewhat stained appearance, are symptoms of Fusarium dieback on this young, severely attacked Acer negundo in Long Beach, CA. Note the grayish halo surrounding beetle entry/exit holes. Barely discernable “toothpick” frass (right center and upper right) is likely from a secondary invader, probably another species of ambrosia beetle (D. R. Hodel). Figure 4. (Right) Advanced symptoms of Fusarium dieback include branch death (Acer negundo, Long Beach, CA). (D. R. Hodel).

TSHBs can be seen at the entry/exit hole openings (Fig. 10) or on freshly cut wood. The host list includes many common The TSHB closely resembles many landscape trees and avocado and other ambrosia beetles. These beetles can be extremely challenging to dif- other fruit trees. ferentiate. Other species of ambrosia beetles, including several species in the genera Monarthrum, Xyleborus, female TSHB, which disperses to attacks the vascular tissue, disrupting and Xyleborinus, are easily mistaken other parts of the host tree or to new water, carbohydrate, and mineral for the TSHB, and their host lists host trees, carries the fungus from flow within the tree, and eventually can overlap with that of the TSHB. tree to tree in specialized sacs in its causing branch die back or, in some These other species can produce dis- head. It secretes the fungal spores cases, death of the entire tree. Some tinctive, solidified frass resembling into its mouth and uses its mandibles potential host species seem capable short, round toothpicks protruding to deposit spores on the walls of the of plugging entry holes with sap and from the bark but, because this frass tunnels it creates. Egg laying and other plant exudates, which may dissolves readily in water, it might hatching are timed to coincide with repel or severely limit movement of be unobserved. Nonetheless, field development of the Fusarium within the beetle and spread of the disease. identification of the TSHB should be the tunnel walls. Larvae remain in the Adult tunneling activity can weaken considered tentative until confirmed tunnels, feeding on the fungus, pupat- branches and provide entry points for by a specialist. ing, and emerging as adults within secondary pests and diseases. about 40 days. Male TSHBs, which The TSHB might be associated Natural history occur at lower rates than females, are with a second fungus, Ceratocystis The disease is the result of the sym- flightless but may crawl out from the fimbriata, which was found on Punica biotic relationship between the TSHB tunnel in which they were reared in granatum (pomegranate) in India but and the Fusarium fungus, a type of order to mate. has not been discovered in California. relationship found in many ambro- The fungus, which is likely de- (C. fimbriata, a vascular wilt disease sia beetles with different fungi. The pendent on the TSHB for dispersal, affecting a wide range of hosts, has

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Table 1. Selected Host Species of the Tea Shot Hole Borer

Botanical Name Common Name Acer negundo box elder

Acer saccharinum silver maple

Ailanthus altissima tree-of-heaven

Albizia julibrissin silk tree

Alnus rubra red alder

Bixa orellana lipstick tree, annatto

Chamaedorea seifrizii bamboo palm

Camellia sinensis tea

Castanopsis spp. chinkapin

Ceiba pentandra kapok

Citrus spp. citrus

Figure 5. Eventually Fusarium dieback Cupaniopsis anacardioides carrot wood will kill the tree (Acer negundo, Long Beach, CA). (D. R. Hodel). Delonix regia royal poinciana Durio zibethinus durian forms or strains with limited host ranges that may ultimately prove to Gmelina arborea beechwood, gamhar be distinct species. One such form, Grevillea robusta silk oak C. fimbriata f. sp. platani, (also known as sycamore canker stain) is found Hevea brasiliensis rubber tree in parts of California but only affects Koelreuteria elegans goldenrain tree trees of the genus Platanus.) Litchi chinensis lychee, litchi

Host List Macadamia integrifolia macadamia nut The host list of the TSHB is over 100 species in 36 families and will likely Mangifera indica mango become longer. The TSHB is a gen- Persea americana avocado, alligator pear eralist (polyphagous), as opposed to having a limited host preference, Persea bombycina som and, therefore, has increased poten- Platanus racemosa California sycamore tial for inflicting greater economic and environmental harm to a wider Platanus × hispanica (Platanus × acerifolia) London plane tree range of hosts. Table 1 lists some of Psidium guajava guava the more commonly attacked species. Preferred or unusually susceptible Punica granatum pomegranate hosts include Persea americana, Acer Ricinus communis castor bean negundo, and Ricinus communis (castor bean). The latter, especially because Robinia pseudoacacia black locust it frequently occurs as a wild plant Shorea spp. meranti along water courses and in unkempt or abandoned areas, might serve as Tectona grandis teak a source of the fungus and vector Terminalia catappa tropical almond for spreading the disease to nearby landscapes and orchards. Theobroma cacao cacao tree Of tremendous concern, of course, is the potential for damage to avocado Wisteria spp. wisteria

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Figure 6. (Left) In some species, a white ring or halo of sugary exudate surrounds the TSHB entry/exit hole (Acer negundo, Long Beach, CA). (D. R. Hodel). Figure 7. (Right) On trees with Fusarium dieback, scraping of the bark down to the wood behind the TSHB entry/exit hole typically reveals brown necrotic tissue (Persea americana). (A. Eskalen). trees and that industry in California. ifornia bay laurel) in the landscape landscape trees, some of which are However, because of the wide host or wild, the species was tested and listed as hosts of the TSHB, included range of the TSHB, potential damage found to be highly susceptible to the Afrocarpus falcatus, Podocarpus gracilior to landscape trees is of equal concern. fungus (U. californica and Persea are in (fern pine), Albizia julibrissin (silk tree), University of California, Riverside the Lauraceae family). Cupaniopsis anacardioides (carrotwood), (UCR) researchers have confirmed In a spectacularly devastating case Geijera parviflora (Australian willow), the disease on various landscape in Long Beach, California in 2010, Grevillea robusta (silk oak), Koelreuteria trees in Los Angeles County. In Israel, where Fusarium dieback severely dam- elegans (goldenrain tree), Liquidambar TSHB and its Fusarium symbiont have aged or destroyed an entire city block styraciflua (American sweet gum), already caused significant economic of Acer negundo street trees, necessitat- Magnolia grandiflora (southern mag- harm. Current research at UCR also ing their removal and replacement, nolia, bull bay), Platanus × hispanica or found that although there are no the TSHB or similar beetle attacked P. × acerifolia (London plane tree), P. known occurrences of TSHB and several other nearby, common land- racemosa (California sycamore), Robinia Fusarium dieback on the California scape trees although there was little or pseudoacacia (black locust), and Ulmus native Umbellularia californica (Cal- no disease development. These other parvifolia (evergreen or Chinese elm).

Figure 8. (Left) Female TSHBs are 0.07 to 0.1 inch long and black. (G. Arakelian). Figure 9. (Right) Male TSHBs are 0.05 inch long and brown. (G. Arakelian).

57 Fall 2012 WESTERN A rborist History trees where they are hatched, it may nia, removal of infested wood from The TSHB was first reported in Cali- be possible to disrupt their breeding the site is prohibited. Although not fornia in 2003, when it was captured with anti-aggregation pheromones. thoroughly evaluated, chipping in- in Lindgren funnel traps in South Consideration is also being given to fested wood or cutting it into 18-inch El Monte. Since 2010 University of finding a parasitoid or other targeted lengths, placing it in a sunny location California and Los Angeles County biological control mechanism. at the site, and tightly covering it with Agricultural Commissioner/Weights clear, heavy plastic for at least three and Measures researchers have de- Management months until the wood is thoroughly tected or identified it and Fusarium Although the TSHB will attack dried and the pest and fungus are dieback on Persea americana and Acer healthy, unstressed trees, maintain- unable to survive might prove to be negundo in southeastern Los Angeles ing trees in optimal health is likely an acceptable management strategy. County. The TSHB has been found the best strategy against TSHB and Prune out any infested or infected mostly along or in the vicinity of the Fusarium dieback. Healthy, vigorous wood at least six inches below symp- Rio Hondo and San Gabriel Rivers, trees might be less attractive to the tomatic areas and sterilize pruning from El Monte to Long Beach. More beetle, are more likely to repel attacks, and other tools with 25% household recently it has been found in Hacienda and would recover from an attack bleach or 70% ethyl alcohol between Heights and La Habra Heights, also more quickly. For optimal tree health cuts. in southeastern Los Angeles County, select species that are well adapted to and in a nursery on Litchi chinensis the site and intended use and plant Donald R. Hodel is the environ- (lychee) in San Diego. The TSHB has and care for them properly. Provide mental horticulture advisor for been in Hawaii since 1975 but the dis- appropriate culture, including ir- the University of California, Coop- ease has not been detected there. rigation, mulch, and, if necessary, erative Extension in Los Angeles. fertilizer. Avoid practices that can Current research stress trees, such as excessive prun- Research is focused on creating a bet- ing, disturbance of the root zone, and Angela Liu is a consulting arborist ter understanding of TSHB and its Fu- too much or too little water. Avoid in Los Angeles. sarium symbiont in order to develop pruning or otherwise wounding trees management strategies. Because the when the weather is warming up and Gevork Arakelian is the entomolo- beetle breeds in the tunnels and on the the beetle becomes active, as they may gist with the Los Angeles County be attracted to fresh wounds. Department of Agricultural Com- Generally, systemic insecticides missioner Weights and Measures. Figure 10. TSHBs can sometimes be applied to soil or injected into roots Akif Eskalen is the extension sub- seen at the entry/exit hole openings or trunks do not control or prevent tropical plant pathologist, Univer- (Acer negundo, Long Beach, CA). (D. attack by ambrosia bark beetles. Insec- sity of California, Riverside. R. Hodel). ticides will not kill the wood-boring stages of most insects. Furthermore, Richard Stouthamer is professor unless a tree is monitored regularly, of entomology, University of Cali- timing of insecticide application is fornia, Riverside. likely to be too late and ineffective. Correctly timed prophylactic bark Editor’s note: spraying, though, using a persistent Senior author Donald R. Hodel has insecticide, might protect a tree from told me that after this article went to further attack although more work press work by University of Califor- is needed on this strategy. Because nia researchers in the Los Angeles TSHB colonizes all branch and trunk area has greatly expanded the list of sizes, the whole tree could be sub- landscape trees that the TSHB attacks, ject to bark treatment. It is currently including several Quercus spp. (oak). unknown how fungicides may work Thus, the TSHB host list is rapidly against the Fusarium. expanding and new, additional infor- Avoid movement of infested mation will be made available on the wood out of infested areas. Scout the website of the UC Riverside Center area for other cultivated host species for Invasive Pest Research. and any wild-growing susceptible Also, at a recent meeting in Riv- hosts, such as Ricinus communis and erside, CA the common name of the Ailanthus altissima. Because the TSHB beetle was changed to the Polypha- is currently a Q-rated pest in Califor- gous Shot-Hole Borer.

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References Arakelian, G. 2012. Tea Shot Hole Borer (Euwallacea fornicatus). County of Los Angeles, Department of Agricul- tural Commissioner/Weights and Measures. CABI. 2012. Invasive Species Compendium. Centre for Agriculture and Biosciences International. On-line: http:// www.cabi.org/isc/compid=5&dsid=57163&loadmodule=datasheet&page=481&site=144. Accessed May 20, 2012. Dreistadt, S. H. 2004. Pests of Landscape Trees and Shrubs, An Integrated Pest Management Guide, 2nd Edition. ANR Publication 3359. University of California, Statewide Integrated Pest Management Program. Oakland, CA. Eskalen, A., A. Gonzales, H. W. Wang, M. Twizeyimana, J. S. Mayorquin, and S. C. Lynch. 2012. First report of Fusarium sp. and its vector tea shot hole borer (Euwallacea fornicatus) causing Fusarium dieback on avocado in California. Plant Disease. On-line: http://dx.doi.org/10.1094/PDIS-03-12-0276-PD. Eskalen, A. and R. Stouthamer. 2012. Pest Alert: Fusarium dieback on California avocado trees vectored by Tea Shot Hole Borer (Euwallacea fornicatus). University of California, Riverside and California Avocado Commis- sion. Mendel, Z., A. Protosav, M. Sharon, A. Zveibil, S. Ben Yahuda, K. O’Donnell, R. Rabaglia, M. Wysoki, and S. Free- man. 2012. An Asian ambrosia beetle Euwallacea fornicatus and its novel symbiotic fungus Fusarium sp. pose a serious threat to Israeli avocado industry. Phytoparasitica: DOI 10.1007/s12600-012-0223-7. Thomas, Michael. 2012. Two Asian Ambrosia Beetles Recently Established in Florida (Curculionidae: Scolyrinae). Pest Alert (DACS-P-01647). Florida Department of Agriculture and Consumer Services, Division of Plant Indus- try. On-line: http://www.freshfromflorida.com/pi/pest-alerts/pdf/two-asian-ambrosia-beetles.pdf. Accessed May 20, 2012.

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